Hemodialysis catheters are implanted into the vasculature of a patient, and have proximal ends that extend from the patient and are connectable to and disconnectable from tubing of a hemodialysis apparatus. Such catheters are provided with a first lumen and a second lumen coextending to respective distal tips that are carefully positioned at a selected site in a particular vessel of the patient, so that undialysed blood may be withdrawn from the patient's vessel while dialysed blood may be reintroduced into the patient's vessel simultaneously, at respective distal tip openings of the lumens. The catheter lumens may be coextending separate catheters or may be dual (or more than two) lumens of a single catheter separated by a septum wall. The distal tips of the two lumens are generally staggered along the vessel such that blood being withdrawn does not include any significant amount of dialyzed blood that has been reintroduced into the vessel at the more distal of the two distal tips.
When a particular dialysis procedure has been completed, the proximal ends of the catheter are disconnected from the tubes of the hemodialysis apparatus, and the lumens are generally inactive until the subsequent dialysis procedure, although fluid medication or saline may be infused into at least one of the lumens, if and when desired, or a blood sample withdrawn. However, blood is highly susceptible to coagulation and clot formation. The addition of a specific agent or locking solution to the catheter or any extracorporeal blood-contacting surface can reduce the incidence of coagulation by interfering and/or inhibiting the hematological chemistry of blood and its interaction with synthetic materials, such as those from which catheters are made.
It is conventional, then, to introduce anticoagulant locking solutions such as heparin into an implanted catheter between hemodialysis treatments, to prevent clotting of blood within the catheter, and which then is withdrawn for the subsequent dialysis procedure. Between hemodialysis treatments, the catheter is clamped off outside of the patient, creating a pressure gradient that holds the locking solution within the lumens. However, certain amounts of locking solution are known to enter the patient's blood stream through the open distal tips, especially in areas where side holes are present. The amounts introduced into the patient are generally not at a level to cause toxicity or disrupt a patient's hematology; however, the leaching of small amounts of locking solution from the distal lumen tips makes the catheter more prone to lumen clot-off.
One catheter assembly directed to minimizing amounts of locking solution entering the patient's blood stream is disclosed in U.S. Patent Publication No. US 2006/0253063 A1. In this application, the catheter includes a first lumen having a first distal tip, and a second lumen having a second distal tip, wherein the first and second distal tips having wall sections that are normally disposed in a closed position but are each openable under fluid pressure. While both lumens have openable distal tip wall sections, the first distal tip has a flap openable both inwardly and outwardly when the first lumen is subjected to negative pressure and positive pressure, respectively, relative to the blood pressure of the patient in whom the catheter has been implanted. The second lumen extends a selected distance distally of the first distal tip to a second distal tip that is a generally rounded tip when closed, and the second distal tip is defined by an openable section that is internally concave and may be formed by at least one slit cut into a closed rounded distal tip after extrusion of the lumen, defining at least two generally curved lip portions.
With respect to the above-discussed catheter system of Publication No. US 2006/0253063 A1, the several lip portions are openable outwardly under positive pressure applied to the distal end of the second lumen, and a closable together under negative pressure applied to the second lumen. Near the second distal tip, in the side wall of the second lumen are side port sections that are openable inwardly upon application of negative pressure to the proximal end of the second lumen. The closable and openable sections of the first and second distal tip sections of the first and second lumens operate thusly: during hemodialysis, negative pressure is applied to the first lumen and blood is drawn from a patient's vessel into the first distal tip and through the first lumen; positive pressure applied to the second lumen when blood enters the proximal end of the second lumen and separates the several lip portions at the second distal tip to re-enter the vessel. Were the reverse of the pressures to be caused by an incorrect hemodialysis connection, blood traveling into the first lumen would open the flap to enter the vessel, while negative pressure on the second lumen would close the several lip sections but open the side ports for blood to enter from the vessel. Between dialysis procedures, locking solution injected under low pressure into the catheter would fill both lumens since the distal tips would be in their closed, undeflected conditions, and when removed, blood from the vessel would enter both distal tips due to negative pressure on both lumens.
It is desired to provide a catheter that will minimize or eliminate the small amounts of locking solution entering a patient's blood stream from an implanted catheter between dialysis treatments.